The present invention relates to a grinding stone which is particularly useful for grinding an object to be ground made of an oxide material (a hard brittle material) such as glass or ceramics. More particularly, it relates to a grinding stone which is a metal-bonded stone using a metal material as the main material of a bonding material, which has a high stock removal rate and which is free from deterioration of the grinding ability due to clogging even in grinding with high precision for a long period of time, and a method for its production and a grinding method employing it.
Usually, a grinding stone is one having abrasive grains of e.g. diamond, cubic boron nitride (hereinafter referred to as xe2x80x9cCBNxe2x80x9d), silicon carbide or aluminum oxide dispersed and fixed in a bonding material. Depending upon the type of the bonding material, it is classified into a resin-bonded grinding stone using a synthetic resin material as the main bonding material material, a metal-bonded grinding stone using a metal material as the main bonding material, and a vitrified grinding stone using a ceramic material as the main bonding material.
Among them, the resin-bonded grinding stone presents a soft touch during grinding, whereby a surface having a proper surface roughness with little defects can be obtained. However, abrasion of the synthetic resin material as the bonding material is remarkable, whereby the useful life of the grinding stone is short. Whereas the metal-bonded grinding stone and a vitrified grinding stone are excellent in the grinding performance and the durability, as their bonding materials have high hardness, and particularly, the metal-bonded grinding stone has the highest grinding ability. However, their stock removal rate is poor particularly against a hard brittle material such as glass or ceramics and the abrading power decreases due to clogging of the grinding stones. Accordingly, to carry out continuous grinding, it is necessary to carry out toothing of the grinding stones frequently i.e. to chip off the surface of the grinding stones to expose a fresh surface to regain the stock removal rate.
In order to solve such problems of conventional metal-bonded grinding stones, for example, JP-A-63-295180 discloses a diamond grinding stone having a high mechanical strength and having a strong sintered structure formed by mixing abrasive grains with iron powder and amorphous carbon powder, followed by press-molding and sintering, and a process for its production (prior art 1). Further, JP-A-7-251378 discloses a porous iron-type metal diamond grinding stone wherein the grinding stone is porous so that the bonding strength of the bonding material is controlled so that in the grinding operation, the bonding material will be abraded properly without resistance thereby to suppress clogging, and the bonding material is an iron type metal, and further, as a bonding material material, carbon is used to control the abrasive grain-holding strength and the mechanical properties of the bonding material portion, and a process for its production (prior art 2).
In the above-mentioned prior arts 1 and 2, the hardness and the bonding strength of the entire grinding stone are increased by using iron or an iron-type metal as the bonding material. Further, it is disclosed that by providing pores in the grinding stone or by adding the carbon component, it is possible to prevent deterioration of the stock removal rate due to clogging, by an autogenous function i.e. scraping of the surface of the grinding stone by a proper degree of grinding, whereby it is possible to obtain a grinding stone which is less susceptible to clogging.
However, according to a verification conducted by the present inventors, since the bonding material which can be used in the prior art 1 or the prior art 2 is limited to iron or its alloy, it is not possible to select a bonding material suitable for an object to be ground, and in some cases, it is not possible to obtain a highly precise treated surface. Further, in the prior art 1, the amount of the carbon powder component which can be added, is limited to a relatively small level, and the autogenous function of the grinding stone can hardly be said to be sufficient. Also the pores in the prior art 2 are limited in the effect of the autogenous function, whereby depending upon the object to be ground or the grinding method, it has been still difficult to maintain a high grinding performance while preventing clogging.
The present invention has been made to solve such problems, and it is an object of the present invention to provide a grinding stone having a high stock removal rate and having an excellent autogenous function not to undergo deterioration of the grinding ability due to clogging even by grinding for a long period of time with high precision, even against an object to be ground made of a hard brittle material, and a process for its production and a grinding method employing it.
The present invention provides a grinding stone using a bonding material made of a metal material as the main material, which comprises:
(A) abrasive grains of at least one member selected from the group consisting of diamond, cubic boron nitride, silicon carbide and aluminum oxide,
(B) a bonding material made of at least one metal member selected from the group consisting of cobalt, nickel and copper, or a bonding material made of an alloy comprising at least one member selected from the group consisting of cobalt, nickel and copper, and at least one member selected from the group consisting of iron, silver, tin, zinc and tungsten, and
(C) amorphous carbon as an adjuvant, wherein the abrasive grains (A) and the amorphous carbon (C) are distributed in the bonding material (B) in a sea-island structure.
Further, the present invention provides a process for producing a grinding stone, which comprises mixing, as the main components:
(a) abrasive grains of at least one member selected from the group consisting of diamond, cubic boron nitride, silicon carbide and aluminum oxide,
(b) a bonding material (b1) made of at least one metal member selected from the group consisting of cobalt, nickel and copper, or a bonding material (b2) made of an alloy comprising at least one member selected from the group consisting of cobalt, nickel and copper, and at least one member selected from the group consisting of iron, silver, tin, zinc and tungsten, and
(c) an adjuvant comprising, as the main material, a synthetic resin material, of which the carbon content remaining after carbonization is at least 50%, compression-molding the mixture into a predetermined grinding stone shape, and sintering the molded product.
Still further, the present invention provides a grinding method which comprises grinding an object to be ground, made of a metal material or an oxide material, by means of the grinding stone as mentioned above.
The present invention also provides a grinding method which comprises grinding an object to be ground, made of a metal material or an oxide material, by means of the grinding stone produced by the process as mentioned above.